Process and apparatus for the treatment of molten ferrous alloys



Feb. 12, 1957 M. c. M. GRANDPIERRE 2,781,250

PROCESS AND APPARATUS FOR THE TREATMENT OF MOLTEN FERROUS ALLOYS 6Sheets-Sheet 1 Filed March 3, 1955 Feb. 12, 1957 M. c. M. GRANDPIERRE2,781,260 PROCESS AND APPARATUS FOR THE TREATMENT OF MOLTEIN FERROUSALLOYS Filed March 3, 1955 6 Sheets-Sheet 2 INVENTOR. MAURICE C Ml'mmafi/sfies Feb. 12, 1957 M. c. M. GRANDPIERRE 2,781,260

PROCESS AND APPARATUS FOR THE. TREATMENT OF MOLTEN FERROUS ALLOYS 6Sheets-Sheet 3 Filed March 3, 1955 UR/CE CM GRA IVDP/ERRE Feb. 12, 1957M. c. M. GRANDPIERRE 2,781,260 PROCESS AND APPARATUS FOR THE TREATMENTOF MOLTEN FERROUS ALLOYS 6 Sheets-Sheet 4 Filed March 3, 1955 INVENTOR.MAUR/CA' C. M 'm wa /wfle ATTOR/V'y Feb 1957 M. c. M. GRANDPIERREPROCESS AND APPARATUS FOR THE TREATMENGP OF MOLTEN FERROUS ALLOYS FiledMarch 3, 1955 6 Shee ts-She et 5:

Feb. 12, 1957 c. M. GRANDPIERRE 2,781,260

PROCESS AND APPARATUS FOR THE TREATMENT OF MOLTEN FERROUS ALLOYS 6Sheets-Sheet 6 Filed March 3, 1955 INVENTOR.

United States Patent fifiee 2,781,260 Patented Feb. 12, 1957 PROCESS ANDAPPARATUS FOR THE TREAT- MENT OF MOLTEN FERROUS ALLOYS Maurice CharlesMarie Grandpierre, P-ont-a-Mousson, Nancy, France, assignor to TheInternational Nickel Company, Inc., New York, N. Y., a corporation ofDelaware Application March 3, 1955, Serial No. 491,820

Claims priority, application France March 6, 1954 18 Claims. (Cl. 75130)The present invention is directed tothe treatment of i a liquid ferrousalloy such as cast iron and steel and, more particularly, to an improvedmethod for introducing into such a liquid ferrous alloy an additionelement having desulfun'zing properties.

It has been heretofore proposed to introduce addition elements havingdesulfurizing properties into liquid ferrous alloys to improve thequality of the resulting castings. it has also been discovered that manyreactive elements having desulfurizing properties when used in thetreatment of molten cast iron have the ability to control graphiteoccurring in the resulting castings to a spheroidal form withaccompanying great improvement in the mechanical properties of thecastings. It has been known that addition elements having desulfurizingproperties, e. g., magnesium, cerium, calcium, etc., are quiteOxidizable and have low boiling points compared with the temperature ofthe liquid ferrous alloy. The result of this is that, in spite of theprecautions that it has already been found possible to take by followingvarious known procedures for introducing these elements, such asoperating in an atmosphere which does not react with the additionelement or by plunging the addition element into the interior of theferrous alloy either with or without the presence of a neutralatmosphere, the losses by volatilization and/ or combustion of theaddition element are considerable. The final result of this is that witha given total quantity of the element introduced, there remains in eachcase and by all known procedures a high degree of uncertainty regardingthe final content of the addition element in the alloy.

To such an extent is this true that, in practice, there are observablein the alloys obtained considerable differencesas between one heat andanother-in behavior and properties. This involves the necessity of apermanent check on every heat and a need to provide considerable marginsof safety.

It has now been discovered that when is introduced into a molten ferrousalloy under highly specialized conditions, the addition reactions areplaced under rigid control With resulting high recovery of the reactiveaddition agents in the molten ferrous alloy.

It is an object of the invention to provide an improved method forintroducing reactive elements into molten ferrous alloys.

It is a further object of the invention to provide a method forintroducing desulfurizing agents into molten cast iron in a particularlyeffective manner.

Another object of the invention is to provide a special apparatusadapted for the purpose of introducing reactive agents havingdesulfurizing properties into molten ferrous alloys.

Other objects and advantages of the invention will become apparent fromthe following description taken in conjunction with the accompanyingdrawings in which:

Figure 1 depicts the design of an apparatus constructed in accordancewith the present invention and adapted for the purpose of introducingreactive desulfurizing agents into molten ferrous metals;

a reactive element F Fig. 2 is a horizontal view of a portion of theapparatus depicted in Figure l with the apparatus being shown in theopen position;

Figure 3 is a view on an enlarged scale of an immersion containerutilized for introducing the reactive addition alloy;

Figure 4 is a partial view in elevation of a first variant with a devicefor stirring by induction;

Figure 5 is a similar view of a second variant;

Figure 6 is a view in perspective of an immersion container of thissecond variant;

Figure 7 is a partial view in elevation of a third variant;

Figures 8 and 9 are horizontal sections along lines VIII-Vlll and IXIXof Figure 7 but on a larger scale;

Figure 10 is an elevation, partly in section, of a further apparatus;

Figure 11 is a section on the line Xl-Xi in Figure 10;

Figure 12 is a section on the line Xil-XII in Figure 10; and

Figure 13 is an elevation of apparatus, essentially as shown in Figure10, mounted on a carriage.

Broadly stated, the present invention is directed to a method forintroducing reactive addition metals having desulfurizing propertiesinto molten ferrous metal while the molten ferrous metal is subjected tosubstantial pressure and while the molten ferrous metal is beingstirred. The pressure utilized in accordance with the inventionpreferably is generated by introducing into the space above the moltenferrous metal a gas under high pressure.

In the invention, the introduction of the addition element is effectedin a closed vessel maintained under a gas pressure at least equal to thevapor pressure of the addition element at the temperature within thevessel so that the addition element is liquefied, and the molten metalis vigorously stirred to mix the liquid addition element with the moltenmetal. The liquefied addition agent will normally fioat on the molteniron or steel, and the stirring ensures that intimate mixing takes placedespite the tendency to float. If more than one addition element is tobe introduced, the pressure in the vessel is maintained above that ofthe addition element with the highest vapor pressure. It is foundpossible in this Way to retain in the solidified metal a greaterproportion of a highly volatile addition agent than has been possiblehitherto, and also to control more effectively than hitherto the actualamount of the addition agent retained in the solidified metal.

The result of this is that it is possible, for a given desired content,to know in advance with an adequate degree of accuracy the total amountof the addition ele ment to be introduced, account being taken ofunavoidable small losses, such as those due to partial evaporation ofsome of the addition element during the course of the treatment andthose due to slight condensations on the walls of the receptacle inwhich the treatment is efiected.

The pressure in the vessel should be very high if the best results areto be obtained. For instance, molten iron to be cast is commonly at atemperature of the order of 1500 C. and at this temperature the vaporpressure of magnesium is about lbs./in. in adding magnesium to molteniron at this temperature, therefore, it is necessary for the pressure tobe higher than 185 lbs./ in. and preferably it is greater than 225lbs/i11 To determine the pressure to be used for a particular additionelement at the desired operating temperature,

' the Clapeyron equation, as given, for example, in Basic log P +5.158

Pressures of this magnitude can easily be set up by introducing acompressed gas into the vessel. The gas used depends on the nature ofthe addition agent. If oxidation of the addition element must beprevented in order to prevent loss, the compressed gas should be inert,being preferably argon or nitrogen, and is recovered from the vesselafter the mixing is complete for the sake of economy. On addingmagnesium to molten iron according to the invention, however, it hassurprisingly been found that if compressed air is used the loss ofmagnesium by oxidation is comparatively small and is more than balancedby the cheapness of compressed air and the simplification of thenecessary apparatus.

A vessel equipped with a stirring device and constructed to withstandthe high pressure involved cannot readily be used as a ladle into whichthe metal is poured. The process is therefore preferably carried out inan apparatus comprising a pressure vessel made in upper and lower parts,the upper part being movable to allow a ladle containing molten metal tobe put in the lower part and thereafter to make a gas-tight closure withthe lower part.

Generally speaking, the apparatus contemplated in accordance with thepresent invention comprises such a pressure vessel or jacket adapted tohold a ladle of the molten ferrous alloy to be treated, said vesselbeing provided with gas-tight opening through which the molten metal tobe treated and the addition material can be introduced, means forapplying gaseous pressure upon the molten metal in said vessel and meansfor stirring the molten metal while said pressure is being appliedthereto.

In order to give those skilled in the art a better understanding of theoperation of the invention as adapted to the apparatus depicted inFigures 1 to 3, the following description is given:

The apparatus includes a pressure vessel 3 consisting of a lower part orbody 6 and an upper part or a lid 11, the body being carried on asupport 5 in a pit 2 which also contains a steel framework 1. The body 6can be raised and lowered by an hydraulic ram 4. The lid 11 is carriedby a frame 12 which can swing in a horizontal plane about a pin 13 inthe top of the framework 1, which is made with a slot 14 engaging with aT-shaped projection 15 on the framework. In the position shown in Figure1 the projection 15 lies in the slot 14, and the frame 12 thereforeholds the lid 11 fixed. The ram forces the body 6 hard against the lid11 to make a pressure-tight joint. In the position shown in Figure 2 theram 4 has been lowered and the frame 12 swung horizontally to give freeaccess to the interior of the body 6 of the vessel.

Operating fluid is supplied to and released from the ram 4 through apipe 7 controlled by a three-way cock 8.

When the vessel 3 is open, a ladle 48 containing molten metal 49 can beput into or removed from the body 6. The bottom of the body 6 isrecessed at 50 to receive and locate the ladle 48.

The lid 11 carries an openwork container 20 for the addition agent, andthis also serves as a stirring device. The container 20 is a bell ofgraphite or of iron with a refractory coating and has openings 21 in itswall. Before the ladle is introduced into the vessel 3, addition agent53, e. g. magnesium in small pieces, is put on an asbestos plate 52, andthis plate is inserted through the open underside of the container andsupported by a grid 22 which is held in position by rods 9. When theladle is in the vessel 3, the container 20 is immersed in the moltenmetal, which then enters the container through the openings 21 andcauses the addition agent to melt and flow out through the openings. 7

To allow the container 26 to be immersed in the molten metal, it iscarried by a rod 19 mounted to slide through the upper part of thevessel and connected externally to a reciprocating piston 10. The rod 19is secured by a collar 42 to a rod 18 which passes through the lid 11and carries the piston in a cylinder 17. This cylinder is fixed in abridge 16 rigid with the frame 12 and so swings with the frame. It isconnected by flexible pipes 23 to a valve 24 which controls the supplyof compressed air from a pipe 25 to the cylinder 17, each end of thecylinder being put under pressure in turn while the other end isexhausted to the atmosphere through a pipe 26. The valve 24 is operatedby a solenoid 27 under to control of a switch 28, opening and closing ofthe switch causing the valve, and therefore the piston 10 and thecontainer 20, to reciprocate vertically.

The apparatus shown in Figure l is designed for operation with anon-oxidizing gas, 6. g. argon. This is supplied from a high-pressurecontainer 32 through a pipe 39 controlled by a valve 31 to an opening 29in the body 6. In order to fill the vessel 3 with argon under highpressure, it is necessary first to expel the air, and this is donethrough an opening 39 in the lid 11, the opening being connected by aflexible pipe 40 to a three-way cock 41 which puts the pipe 40 intocommunication with the atmosphere during the air expulsion andsubsequently is closed.

It will now be appreciated that the sequence of opera tions is to chargethe container 20; insert the ladle 48 containing the molten metal 49 inthe vessel 3; close the vessel by swinging the frame 12 and then operatethe ram 4; expel the air by opening the valve 31 and turn the cock 41 toexhaust the air to atmosphere; close the cock 41 to allow the pressurein the vessel 3 to build up to the desired high value; close the switch28 to lower the container 20 into the molten metal; and then repeatedlyopen and close the switch 28 to cause the container 20 to reciprocateand stir the molten metal so as to mix the addition agent with it.

When the liquid metal makes contact with the addition element orelements, the latter melts with a tendency to evaporation. As, however,the pressure in the container is greater than the vapor pressure of thiselement at the temperature under consideration, it remains liquid. Owingto its low density, compared with that of the alloy being treated, theliquid element tends to float and it is the successive dippings of thecontainer 20 into the metal which ensure the intimate mixing of the saidelement with the whole of the alloy contained in the ladle.

When the mixing is complete, the valve 31 is closed. Before opening thevessel 3 to remove the ladle and cast the metal it is necessary torelease the pressure and recover as much as possible of the argon. Thisis done by turning the cock 41 to put the vessel 3 into communicationwith a low-pressure gas reservoir 44 of large capacity through a pipe 43and then turning the cock 41 to the closed position again. Thereafterthe vessel 3 is opened, the ladle is removed and the metal is cast.

To enable the argon to be used again, a valve 46 in a pipe 47 leadingfrom the reservoir 44 to a compressor 38 is opened and the compressor isstarted. The compressor forces the argon through a pipe 37 controlled bya threeway cock 33 into the cylinder 32. Additional argon to make up forlosses can be supplied through a pipe 35 and the cock 33.

To illustrate the importance of the high pressure, the results of someprocesses carried out in an apparatus as shown in Figure 1 will now begiven as Tests I to III and Examples IV and V, Tests I to IIIillustrating the effects when the pressure, even though high, is not ashigh as is required by the invention, and Examples IV and V beingexamples of the invention. In each case magnesium was added to molteniron, and the final contents of magnesium and sulfur retained in theiron as cast were determined. Assuming that all the sulfur removed fromthe iron reacted with the magnesium, the recovery of magnesium, i. e.the percentage of the added magnesium accounted for, can be expressed asfollows: Percent recovery:

Percent retained Mg+ (initial percent S-final percent S) Percent addedMg Test I The molten iron contained:

C Si Mn P S Percent Percent Percent Percent Percent 3. 75 1. 70 0.08 0.04 0. 032

The temperature of the iron when introduced into the ladle 48 was 1440"C. as read from an optical pyrometer without compensation for emissivity(i. e. a true temperature of about 1500 C.). The mixing operation lasted2 minutes, the argon pressure being maintained between 42 and 75lbs./in. During this time the container 20 plunged up and down fifteentimes. The temperature of the iron at the end of the operation was 1315C. (as read). Analysis of the iron showed that the amount of magnesiumretained was 0.01%, and the sulfur content was 0.017%. Microscopicexamination revealed a flake graphite structure and mechanicalproperties equivalent to those of an ordinary gray cast iron. Themagnesium recovery was 21%.

Test II The molten iron contained:

(3 Si Mn P f S I Percent Percent Percent Percent Percent The temperature(as read) of the iron at the start of the operation was 1420 C. Mixinglasted 1 /2 minutes, the argon pressure being held between 130 and 145lbs./in. i. e., still well below the vapor pressure of magnesium at thetemperature of the iron. The retained magnesium content was 0.01% andthe final sulfur content 0.008%. The magnesium recovery was thus 23%,and the graphite was in flake form.

Test III The molten iron contained:

o St I Mn I P s i Percent Percent Percent Percent Percent Example IV Themolten iron contained:

l C 1 Si Mn 1 i S 1 Percent Percent] Percent Percent Percent 3. 74 1. 700. 08 0. 04 0. 036

The temperature (as read) of the iron at the start of the operation was1465" C. The operation lasted 2 minutes with an argon pressure between225 and 268 lbs./in.

i. e., a pressure greater than the vapor pressure of magnesium. Thefinal temperature (as read) was 1300 C. This iron was inoculated with 1%of ferro-silicon (75% Si) which gave a final silicon content of 2.43%.The retained magnesium content of the cast iron was 0.04% .and the finalsulfur content 0.007%. The magnesium recovery was thus 62% and thegraphite was spheroidal.

A test piece 25 mm. thick, cast in dry sand from the inoculated iron,had a tensile strength, as cast, of 76 leg/mm. (48 tons/m an elongationat fracture of 4% and a Brinell hardness of 229.

Example V The molten iron contained:

The temperature (as read) of the iron at the start of the operation was1470 C. The operation lasted 2 minutes in a nitrogen atmosphere, thepressure of which was be tween 225 and 254 lbs./in. 1 ie retainedmagnesium content was 0.05% and the sulfur content 0.007%. The recoverywas thus 68%, and microscopic examination showed spheroidal graphite.The mechanical properties of the iron, as cast, were approximatelyequivalent to those of the iron obtained in Example IV.

The above-cited Examples I V and V show that application of thisprocedure in accordance with the invention enables contents of magnesiumto be obtained which ensure the presence of graphite in spheroidal formin cast iron as a result of quite small additions (0.10%) of magnesiumto molten cast iron. Furthermore, the use of magnesium in the pure stateensures economical manufacture. The tests and examples also show clearlythat the results desired are only obtained with a treating pressurewhich is at least equal to the vapor pressure of the addition element atthe temperature of the treatment. Those skilled in the art willappreciate that the maximum pressure employed is a practicalconsideration influenced by the strength of the materials used in theapparatus an the requirements of the particular application.

Stirring of the cast iron or other ferrous alloy during treatment can,or" course, be effected by other means than that described in the courseof Test I. There is shown in Figure 4 a first variant in which stirringis obtained by electrical induction, a device already known as such. Forthis to be done, the vessel 3 is provided inside with a winding 54suitably insulated from the wall of the container and connected with ahigh frequency generator 55. The rest of the apparatus is identical withthat in Figure 1. It may be noted that, in view of the stirring obtainedby means of the winding 54, it is not necessary duringthe treatment tomove the bell containing the addition element or elements.

Figures 5 and 6 illustrates another variant in which the container 20 iscarried by a shaft 34 mounted to slide through the upper part of thevessel and externally connected to a motor 56, so that the container canbe rotated within the metal 49. To ensure adequate stirring thecontainer 20 is provided with vanes 57. The motor 56 and shaft 34 can bemoved up and down as a unit by a piston 10 on a shaft 18 secured to aframe 36 in which the motor is mounted. In this variant the rest of theapparatus is identical with that in Figure 1.

Figures 7 to 9 illustrate another variant in which the vessel 3 hasdimensions enabling it to receive two ladles, one on top of the other.The molten metal is allowed to run out of the upper ladle 62 onto piecesof magnesium 53 in the lower ladle 53. These pieces are held down by aperforated plate 60 with peripheral notches 61 shaped,

' to pass axially past lugs 59, the plate, after partial rotation, beingheld by the lugs against axial movement.

The molten metal in the upper ladle 62 can pass through a hole in thebottom of the ladle when a plug 63 is removed. This plug is in positionwhen the ladle is put in the vessel 3 and its upper end is pivoted to alever 64. This lever is pivoted on the ladle 62, and after the ladle hasbeen put in the vessel 3 the free end of the lever 64 is in contact witha disc 65 on a rod 19 similar to the rod 19 in Figure 1. Then downwardmovement of the disc 65 rocks the lever and lifts the plug 63. The metalflows into the ladle 58 and the magnesium retained by the plate 60 meltsprogressively, flowing through the metal, which is stirred by thefurther metal entering from the ladle 62.

When compressed air can be used to set up the pressure, it is possibleto use the much simpler apparatus shown in Figures 10 to 13. This alsoincludes yet another form of stirring device.

in this apparatus a pressure vessel T consists of a relatively shallowlower part and a relatively large upper part 109. The lower part 101 hasa refractory lining T02 and lugs 103 which locate and support a ladle 48containing molten metal 49. The upper edge of the part 101 isfrusto-conical as shown at 107 to mate with a complementary surface onthe upper part 109, which carries a heat-resistant packing 113 to ensurea tight joint between the two mating surfaces. The part 19? has a flange110 and the lower part 101 has lugs 103. A ring 114, U-shaped incross-section, surrounds the flange 110 and the lower arm of the U isrecessed to clear the lugs 10% on axial movement. On turning the ring114 the lower arm of the U engages beneath the lugs 108 to hold theparts 101 and 109 together. The engaging surfaces of the ring 114 andlugs 103 are slightly inclined to produce a wedging action when the ring114 is turned.

The ring 114 is turned mechanically by a pneumatic ram 115 having acasing connected by a lever 116 to the part 109 and a plunger 117connected to the ring at 118. The stroke of the ram plunger is such asto bring the ring either into the position in which the lug 108 can passthrough the recesses in the ring or into the position in which the parts101 and 109 of the vessel are urged towards one another to the maximumextent.

The upper part 109 of the vessel in this apparatus has a throat 120leading to a compartment 119 closed by a cover plate 121 and housing arod 122 carrying a stirring device 126. This device is a disc anddiffers essentially from the device of Figure 1 in that it does notcontain the addition agent. The addition agent 150, in stick form, isintroduced into the part 109 through an opening 141 above the disc 126while the disc is in its uppermost position shown in dotted lines. Thedisc supports the addition agent 150 and keeps it from falling into themolten metal 49 until the disc is moved downwards. The opening 141 isclosed by a cover plate 142.

The stirring device 126, the rod 122 of which has a refractory covering127 and carries a centering collar 125, is articulated to a double-armedlever 123 which is rigid with a pivot mounting 124 which passes influid-tight fashion through the upper part 109 of the vessel. The lever123 carries a counterweight 129 and is rocked by an hydraulic ram 131pivotally mounted on the outside of the upper part 109 of the vesselwith its plunger pivotally connected to the lever 123. It will be seenthat by causing the ram to reciprocate, the stirring device 126 is firstmoved downward to allow the addition agent 150 to fall into the ladle 48and then is moved up and down with some rocking movement in the moltenmetal, to stir it. To ensure that a magnesium addition agent willreadily dissolve in molten iron, the speed of movement of the disc 126should be about 6 inches per second.

A compressed air reservoir 1.34 is mounted on a bracket 133 on the part109 and is fed through a pipe 135 controlled by a valve 136. Thisreservoir is connected to the interior of the vessel 100 by a passage137 of substantial cross-section, controlled by a valve 138. The size ofthis passage allows the vessel to be put under pressure quickly.

At the end of the mixing the pressure can be released by opening a valve140 in an outlet 139 also of substantial cross-section.

The upper part 109 of the vessel can be lifted by a hook on the end of acable 143 which carries a counterweight 144 and runs over a pulley 146and a dmm 147 on a rotary beam 148. The drum 147 can be turned by anelectric motor 128. The beam 148 which supports the cable can turn on apillar 149. The upper part 109 can therefore be lowered in successiononto different lower parts 101 arranged around the pillar 149, eachlower part containing a ladle of molten metal to be treated. Figure 13shows two lower vessel parts 101A and 101B mounted on a carriage 151which can run between end positions determined by chocks 152 and 153 tobring each lower part in turn beneath an upper part 109 arranged to belifted and lowered by a lifted mechanism fixed in position.

The apparatus shown in Figures 10 to 13 presents the advantage that thetime taken by the operations preliminary to the treatment proper withthe addition agent is very considerably reduced and thus the metal is ata higher temperature for casting when the mixing is complete. Moreover,with energetic stirring by the device 126 the time of mixing is alsoreduced, say to 1 minute or 1 /4 minutes, thus reducing the loss ofaddition agent by oxidation and by condensation on the walls of thepressure vessel.

The results of two processes carried out according to the invention withthe apparatus shown in Figtue 10 will now be given. As in the earliertests and examples, 200 grams of magnesium were added to 200 kgs. ofmolten iron in each case.

Example VI The molten iron contained:

0 Si Mn P S m-- Per- Per- Percent cent cent cent Percent 3. 85 1. 72 0.05 0.05 0. 010

Example VII The molten iron contained:

0 Si Mn P S Per- Per- Par- Percent cent cent mu Percent 3. 6 1. 7 0. 070. 04 0. 019

The temperature (as read) when the vessel was closed was 1430 C. Thetotal duration of the operation was 2 /2 minutes, the mixing occupyingone minute, and the air pressure was between 239 and 268 lbs./in. Thefinal temperature (as read) was 1370 C., the fall in temperature beingthus only 60 C. The retained magnesium content was 0.049% and the finalsulfur content 0.008%, so the magnesium recovery was 57%. All thegraphite was spheroidal.

The apparatus may be modified further in that the lower part may be nomore than a plate-like support for a ladle, and the upper part may be abell wholly surrounding the ladle.

Naturally if the apparatus shown in Figures to 13 is to be used with anon-oxidising gas, a gas-recovery system similar to that shown in Figure1 may be added.

The method and apparatus contemplated in accordance with the inventionmay be used for the purpose of de sulfurizing ferrous alloys or may beused for the purpose of producing alloys of ferrous metals, such as castiron and steel containing one or more metals, having desulfunizingproperties in ferrous metal. As has previously been mentioned herein,magnesium, calcium and cerium are elements having such desulfurizingproperties. Those skilled in the art will appreciate that other membersof the alkali and alkaline earth metal groups, etc, also are recognizedto have such desulfurizing properties, These metals all have meltingpoints lower than that of iron. It will be appreciated that whendesulfurization is the primary object then quite small amounts of thereactive elements may be employed. Thus, in the case of magnesium, anamount of magnesium approximately equal on a weight basis to the amountof sulfur in the metal, e. g., cast iron being treated, is usuallysufiicient to effect desulfurization. When it is desired to producealloys containing the reactive metal then somewhat larger additions ofreactive metal are employed. For example, in the case of magnesium,amounts of magnesium on the order of up to about 0.5% may be added tothe molten cast iron in accordance with the present invention.

Although the present invention has been described in conjunction withpreferred embodiments, it is to be understood that modifications andvariations may be resorted to without departing from the spirit andscope of the invention, as those skilled in the art will readilyunderstand. Such modifications and variations are considered to bewithin the purview and scope of the invention and appended claims.

I claim:

1. The method for introducing a reactive metal into a molten ferrousalloy which comprises applying to a bath of said molten alloy a gaspressure at least equal to the vapor pressure of the reactive metal atthe temperature of said molten alloy, inserting a reactive metal beneaththe surface of said molten alloy and energetically stirring said moltenalloy in contact with said reactive metal until substantially all ofsaid reactive metal has become incorporated in said molten alloy.

2. The method for alloying molten metal from the group consisting ofcast iron and steel with a reactive metal from the group consisting ofmagnesium, calcium and cerium which comprises establishing a bath ofmetal from the group consisting of cast iron and steel, applying to saidbath a gas pressure at least equal to the vapor pressure at thetemperature of said bath of the reactive metal added, inserting areactive metal from the group consisting of magnesium, calcium andcerium into said bath and energetically stirring said bath whilemaintaining said pressure for suflicient time to incorporate saidreactive metal substantially in said bath.

3. The process for introducing magnesium into molten cast iron whichcomprises establishing a bath of molten cast iron, applying thereto agas pressure at least equal to about the vapor pressure of magnesium atthe temperature of said molten cast iron, inserting magnesium into saidmolten bath and agitating said bath while applying gas pressure theretountil the alloying of magnesium with the molten cast iron is effected.

4. The process for introducing magnesium into molten cast iron whichcomprise establishing a bath of molten cast iron, applying thereto anair pressure at least equal to about the vapor pressure of magnesium atthe temperature of said molten cast iron, inserting magnesium into saidmolten bath and agitating said bath While applying 10 said air pressurethereto until the alloying of magnesium with the molten cast iron ieffected.

5. The process for introducing magnesium into molten cast iron whichcomprises establishing a bath of molten cast iron, applying thereto asubstantially non-oxidizing gas at a pressure at least equal to aboutthe vapor pressure of magnesium at the temperature of said molten castiron, inserting magnesium into said molten bath and agitating said bathwhile applying said gas pressure thereto until the alloying of magnesiumwith the molten cast iron is effected.

6. The process for introducing magnesium into molten cast iron whichcomprises establishing a bath of molten cast iron, applying theretoargon gas at a pressure at least equal to about the vapor pressure ofmagnesium at the temperature of said molten cast iron, insertingmagnesium into said molten bath and agitating said bath while applyingpressure thereto until the alloying of magnesium with the molten castiron is elfected.

7. The process for introducing magnesium into molten cast iron whichcomprises establishing a bath of molten cast iron, applying thereto airat a pressure of at least about 225 lbs. per square inch, insertingmagnesium into said molten cast iron and agitating said molten cast ironwhile maintaining said pressure until said magnesium is alloyed withsaid molten cast iron.

8. An apparatus adapted for the treatment of molten metal under pressureof a gas whereby said gas may be recovered which comprises, incombination, a pressure vessel adapted to hold molten metal, a source ofhighpressure gas connected to said pressure vessel by a control valve, alow-pressure reservoir connected to said pressure vessel by a controlvalve and a compressor connected between said low-pressure reservoir andsaid highpressure source, said compressor being adapted to pump gas fromsaid low-pressure reservoir to said high-pressure source and thereby torecover gas received in said low-pressure reservoir.

9. An apparatus particularly adapted for the introduction of reactivemetals into molten ferrous melts and comprising, in combination, apressure vessel having an opening provided with a gas-tight closure, acontainer for holding molten metal disposed within said vessel, meansfor introducing gas under high pressure into said vessel, means forcontrollably introducing addition material below the surface of moltenmetal held in said vessel, and a high-frequency induction coil disposedabout the molten metal container whereby stirring is effected byelectromagnetic induction.

lO. An apparatus adapted for the treatment of molten metal comprising,in combination, a vessel having a lid and being adapted to hold moltenmetal under pressure, means for supplying gas pressure within saidvessel, and a receptacle disposed within said vessel and adapted to holdaddition material, said receptacle being provided with outer vanes andbeing connected through said lid with means for imparting rotationalmotion to said receptacle.

11. An apparatus adapted for the treatment of molten metal underpressure which comprises, in combination, a pressure vessel adapted tohold molten metal, a source of high-pressure gas connected to saidvessel, and mixing means disposed within the pressure vessel and havingtwo ladles placed one atop the other, with the lower ladle adaptedinitially to contain addition material, and with the upper ladle beingprovided with a stopper openable from without the vessel.

12. An apparatus adapted for the introduction of reactive metals intomolten ferrous alloys and comprising a pressure vessel made in upper andlower parts, the upper part being removable to allow a ladle containingmolten metal to be placed in a lower part and thereafter to make agas-tight closure with said lower part, means for placing the interiorof the closed vessel under gas pressure, means for introducing anaddition element into the metal '11 in the ladle after the closing ofthe vessel, and means for bringing aboutvigorous stirring of the metalin theladle while the vessel is closed, the stirring means beinga discmounted in its uppermost position to support an addition agentintroduced through an opening above it, whereby on downward movement ofthe disc the addition agent is allowed to enter the metal and the metalis stirred by the disc.

13. An apparatus adapted for the introduction of reactive metals intomolten ferrous alloys and comprising a pressure vesselmade in upper andlower parts, the upper part being removable to allow aladle containingmolten metal to be placed in a lower part and thereafter to make agas-tight closure with said lower part, means for placing the. interiorof the .closed vessel under gas pressure, means for introducing anaddition element into the metal llIl the ladle afterthe closing of thevessel, and means for bringing. about vigorous stirring of the metal inthe ladle while the vessel is closed, the stirring means beingarticulated to a double-armed lever having a pivot mounting which passesthrough theupper part of the vessel, the lever being rockedby adeviceitself mounted on the outside of the upper part of the vessel.

14. An apparatus adapted for the introduction of reactive metals intomolten ferrous alloys and comprising a pressure vessel made in upper andlower parts, the upper part being removable to allow a. ladle containingmolten metal to be placed in a lower part and thereafter to make agas-tight closure with said lower part, means for placing the interiorof the closed vessel under gas pressure, means for introducing anaddition element into the metal in the ladle after the closing of thevessel, and means for bringing about vigorous stirring of the metal inthe ladle 'while the vessel is closed, the upper part of the vesselbeing engageable by a hook on a lifting cable carried by a rotarysupport, whereby the upper partcan be lowered onto different lower partsin succession.

15. An apparatus adapted for the introduction of reactive metals intomolten ferrous alloys and comprising a pressure vessel made in upper andlower parts, the upper part being removable to allow a ladle containingmolten metal to be placed in a lower part and thereafter to make agas-tight closure with said lower part, means for placing the interiorof the closed vessel under gas pressure,

means for introducing an addition element into the metal inthe ladleafter the closing of the vessel, and means for bringing about vigorousstirring of the metal in the ladle while the vessel is closed, two ormore lower vessel parts being mounted on a carriage which carries themin turn beneath a single upper part.

16. An apparatus adapted for the introduction of reactive metals intomolten ferrous alloys and comprising a pressure vessel made in upper andlower parts, the upper part being removable to allow a ladle containingmolten metal to be placed in a lower part and thereafter to make agas-tight closure with said lower part, means for placing the interiorof the closed vessel under gas pressure, means for introducing anaddition element into the metal in the ladle after the closing of thevessel, and means for bringing about vigorous stirring of the metal inthe ladle while the vessel is closed, the upper and lower parts of thevessel presenting conical mating surfaces, one of which is recessed toreceive a packing.

17. An apparatus adapted for the introduction of reactive metals intomolten ferrous alloys and comprising a pressure vessel made in upper andlower parts, the upper part being removable to allow a ladle containingmolten metal to be placed in a lower part and thereafter to make agas-tight closure with said lower part, means for placing the interiorof the closed vessel under gas pressure, means for introducing anaddition element into the metal in the ladle after the closing of thevessel, and means for bringing about vigorous stirring of the metal inthe ladle while the vessel is closed, the two parts of the vesselinterengaging by relative axial movement followed by rotary movement ofa locking ring on one part into engagement with fixed lugs on the otherpart, and a poweractuated device being provided on the first part toturn the locking ring.

18. The process for introducing magnesium into molten cast iron whichcomprises establishing a bath of molten cast iron, applying thereto airat a pressure of at least about 185 pounds per square inch, insertingmagnesium into said molten cast iron and agitating said molten cast ironwhile maintaining said pressure until said magnesium is alloyed withsaid molten cast iron.

References Cited in the file of this patent UNITED STATES PATENTS Re.13,849 Simpson Dec. 15, 19l4 1,707,161 Hoy Mar. 26, 1929 1,808,145Machlet June 2, 1931 2,485,760 Millis et al. Oct. 25, 1949

1. THE METHOD FOR INTRODUCING A REACTIVE METAL INTO A MOLTEN FERROUSALLOY WHICH COMPRISES APPLYING TO A BATH OF SAID MOLTEN ALLOY A GASPRESSURE AT LEAST EQUAL TO THE VAPOR PRESSURE OF THE REACTIVE METAL ATTHE TEMPERATURE OF SAID MOLTEN ALLOY, INSERTING A REACTIVE METAL BENEATHTHE SURFACE OF SAID MOLTEN ALLOY AND ENERGETICALLY STIRRING SAID MOLTENALLOY IN CONTACT WITH SAID REACTIVE METAL UNTIL SUBSTANTIALLY ALL OFSAID REACTIVE METAL HAS BECOME INCORPORATED IN SAID MOLTEN ALLOY.